Surface characterization of plasma-modified poplar veneer: Dynamic wettability

Abstract

The dynamic wettability of plasma-modified poplar veneer was investigated with sessile adhesive droplets using a wetting model. Dynamic contact angle, instantaneous and equilibrium contact angles, and their rates of change (K-value) were used to illustrate the dynamic wetting process. The experiment consisted of selecting treatment parameters (type of gas, power) that would lead to the increased wettability of wood. Three resin systems, urea-formaldehyde (UF), phenol-formaldehyde (PF), and diphenylmethylene diisocyanate (MDI), were evaluated. Based on the wetting model, the K-value was used to interpret the kinetics of wetting. The higher the K-value, the faster the contact angle reaches equilibrium, and the faster the liquid penetrates and spreads. Therefore, the model was helpful for characterizing the dynamic wettability of wood surfaces modified with different plasma treatments. The K-values of plasma-treated veneer surfaces at different plasma power levels and with different gases (such as O2, N2, Ar, air, and NH3) were 458% to 653% and 332% to 528% higher than those of untreated veneer surfaces, respectively. In addition, the K-values of the three resins on the oxygen plasma-treated veneer surfaces were 38% to 1204% higher than those on the untreated veneer surfaces. Therefore, this method was helpful for characterizing the dynamic wettability of veneer surfaces modified with plasma treatment.